The teachings presented herein relate generally to calibration of output devices. The teachings presented herein relate more specifically to calibration of color displays.
An ever increasing number of presentations today are given electronically using projection display technology. However, in such presentations, color images often do not reproduce correctly due to lack of projector calibration. In cases where the color imagery is intended to convey an important message, this problem can severely diminish the value of a presentation. Examples include technical, educational, and marketing presentations attempting to demonstrate color and image quality effects. Readability of text and other details are often compromised as well, and often the presenter is compelled to apologize, insisting, “It looked good on my computer screen.”
A standard approach for determining the projector's tone response is to make device-independent measurements of R, G, B ramps with a spectroradiometer, and then derive a tone response function that relates digital input value to luminance by fitting or interpolating the measured data. This type of approach can be expected to produce a highly accurate correction. However, making spectroradiometric measurements is a very expensive, time-consuming and tedious process. Indeed this is the reason why projection display calibration is typically avoided, and users simply live with and otherwise tolerate the erroneous result.
What is needed is a straight forward easy to perform calibration for projection displays which does not require expensive test equipment or special involved operator skills or training to accomplish.
Disclosed in embodiments herein is a method of correcting colors input to an output device comprising, rendering a target of color patches of known input values on the output device, and capturing an image of the target with a digital camera. This is followed by extracting camera signals from the captured image corresponding to the color patches, and deriving a tone response calibration for the output device from the camera signals and the known input values.
Further disclosed in embodiments herein is a method of color correction for a display device comprising, displaying a target of patches of known input values on the display device; and capturing an image of the target of patches with a digital camera. This is followed by calibrating the digital camera as based upon the captured image of the target patches; extracting calibrated camera signals from the captured image of the target of patches, the extracted calibrated camera signals corresponding to the patches in the target of patches; and deriving a tone response calibration for the display device from the extracted calibrated camera signals and the known input values.
Further disclosed in embodiments herein is a method of color correction for a display device comprising, displaying a visual graphical user interface pattern, determining an intermediate luminance point as based upon user input in reaction to the visual graphical user interface pattern, and displaying a ramp target of patches of known input values including the determined intermediate luminance point on the display device. This is followed by capturing an image of the ramp target of patches with a digital camera, and calibrating the digital camera as based upon the captured image of the ramp target patches and the determined intermediate luminance point. That is followed by extracting calibrated camera signals from the captured image of the ramp target of patches, the extracted calibrated camera signals corresponding to the patches in the ramp target of patches, and deriving a tone response calibration for the display device from the extracted calibrated camera signals and the known input values.